Whole-number spreads can push (a -3 favorite winning by exactly 3 refunds both sides); half-point lines cannot. In the NFL the distribution of final margins clusters on 3 and 7, so half-points around those “key numbers” carry real value - the entire logic of teasers and spread middles lives there.
Spreads are market key spreads, with each outcome carrying its point value alongside the price. Alternate numbers are exposed as alt-line markets in the catalog at /v1/meta/markets. Cross-book spread comparison - both the number and the price on it - is the core of best-line shopping.